The present invention relates to an aircraft weight and balance system and more particularly to a weight and balance system which automatically compensates for loading errors while the aircraft is stationary.
Before each flight, the weight and balance of an aircraft must be determined to insure that they are within safe operating limits. This is typically accomplished by estimating the total aircraft weight when loaded and the distribution of that weight in order to determine the aircraft's center of gravity or balance.
To insure proper distribution of the weight, onboard weight and balance systems for aircrafts have been developed which calculate the weight and center of gravity of the aircraft in response to various sensor signals. Known weight and balance systems using strain gauges and pressure or magnetic variable reluctance sensors have been found to be unreliable due to problems in the sensor's stability, accuracy, and ability to survive harsh environments.
A known weight and balance system which overcomes the above problems is shown in Bateman, U.S. Pat. No. 4,312,042. This system uses inclinometers positioned to measure the angle of bending in a structural member, such as the landing gear of the aircraft, where the angle of bending is proportional to the weight or force on the member. The inclinometers provide output signals which are summed to cancel out attitude and acceleration changes, whereby only that portion of the angle of bending corresponding to weight is obtained. When the aircraft is stationary and being loaded and unloaded, it has been found that moments are created which constrain the bending of the structural member on which the inclinometers are mounted so that an error results in the calculated weight derived from the inclinometer outputs. Although the moments constraining the bending of the landing gear members are virtually eliminated once the aircraft is moved so that the members deflect to their true unconstrained value resulting in an accurate weight determination, it is impractial to require that the aircraft be moved after loading in order to determine whether its weight and balance are within the safety limits.